1. FIELD OF THE INVENTION
This invention relates generally to diapers and more particularly to an improved disposable diaper provided with sealing strips and to a method of manufacture thereof.
2. DESCRIPTION OF THE PRIOR ART
Conventional disposable diapers comprise a rectangular back sheet of waterproof material, a rectangular absorbent pad and a rectangular top sheet of hydrophobic material. The back sheet is generally wider than the pad and the top or face sheet and the longitudinal edges of the back sheet extend past the longitudinal edges of the pad and the top sheet. The back sheet is folded around the edges of the pad and onto the top sheet. The longitudinal edges of the back sheet are then adhered to the top sheet. Conventional disposable diapers are prepared in one of a number of prefolded configurations to permit the disposable diaper to have a narrowed portion in order to make the disposable diaper more closely adapted to fit the trunk and thighs of an infant than if the disposable diaper was applied in a non-prefolded rectangular configuration.
In order to successfully meet consumer expectations a disposable diaper must, as an assembly, have sufficient strength to prevent tearing when applied and when worn by an infant and must also have sufficient limpness or ability to be molded or adjusted by hand to fit closely around the thighs and trunk of an infant. This limpness, or ability to be molded or adjusted by hand, is required in order to create a seal to contain discharged urine in order to give the absorbent pad sufficient time to absorb the urine. Failure to provide these features results in a product which causes soiled clothing, infant discomfort and a general reaction on the part of the consumer that the product is not effective.
Present disposable diapers attempt to meet the above goal of having sufficient strength to avoid tearing by providing the above mentioned folded edge of back sheet on each of the longitudinal edges of the diaper. The back sheet on one form of conventional disposable diaper has two side flaps which are folded, one each, around the longitudinal edges of the absorbent pad and are fastened to the face sheet by adhesive. In this form of conventional disposable diaper the combined width of the two side flaps which are folded onto the top sheet are equal to approximately two thirds of the overall width of the diaper in the folded configuration. This double layer of back sheet material along the longitudinal edges of the diaper is required because the tensile forces created when applying a disposable diaper are sufficiently large so as to deform or tear the back sheet if a single layer back sheet is used at the longitudinal edges of the diaper. The folded portion of the back sheet are placed in a complex state of combined bending and tensile stress when the conventional disposable diaper is applied. This results in local buckling and bulging of the back sheet away from the thighs and trunk of the infant with consequent loss of sealing contact.
Another disadvantage of present conventional disposable diapers is that the folding of the back sheet over the edge of the absorbent pad prevents air from contacting the edge of the pad. The consequent thermal insulation of the edges of the pad by the back sheet contributes to the absorbent pad retaining the head produced by the absorption and accumulation of waste products and also retaining body heat. This heat retaining property of conventional disposable diapers is undesirable since it leads to infant discomfort. In addition to the undesireable effects in conventional disposable diapers related to the two portions of the back sheet which cover the longitudinal edges of the pad, additional undesirable effects are related to the side flap portions of the back sheet which overlay the face sheet. These portions of the backsheet contribute to the undesirable thermal insulating properties of the conventional disposable diaper. In addition, when the conventional disposable diaper is applied to an infant, the side flap portions form a relatively large portion of the overall width of the diaper in the narrow crotch area. The side flap portions prevent absorption of waste products through the hydrophobic face sheet in those covered areas and actually increase dripping of excess fluid. In addition, in the crotch area, those portions of the back sheet which overlay the top sheet, since they form a relatively large portion of the overall disposable diaper width, readily become wet with urine and cause infant discomfort. In certain cases these wet portions at the edges of the side flaps in contact with the infant's skin can lead to skin rashes and other skin disorders caused by the combined effects of urine and body heat.
A rectangular diaper is disclosed in the U.S. Pat. No. 3,592,194 issued to Robert C. Duncan on July 13, 1971 for DIAPER HAVING IMPROVED WICKING AND DRYNESS. This rectangular diaper is folded in a box pleat such as also disclosed in British Pat. No. 1,011,888 of Dec. 1, 1965. However, the panels defined by the box pleated diaper are spaced substantially from each other requiring that the central panel behind the pleated panels receive most of the urine while the spaced apart panels provided with side flaps also permit chaffing.
Further, in order to provide the desired absorptive capacity, the rectangular diaper with the spaced apart panels is of an undue width which allows the legs to force the diaper down so that it tends to sag away from the trunk of the body thus preventing proper utilization of the absorptive capabilities of the diaper.
In addition, in the prior art rectangular diapers because of the spaced-apart position of the folded panels of the diaper, surface wetness of the hydrophobic face sheet of the central portion or panel of the diaper resulting from the inefficient transfer of waste fluids from the center into the total mass of absorbent material is prevelant because of the space-apart position of the folded panels which results in a wetting of the face sheet adjacent the skin of the infant, thus reducing the advantages otherwise inherent in the use of a hydrophobic face sheet because instead of small areas which have been wet while permitting passage into the hydrophilic or absorbent pad, substantially the entire surface area of the hydrophobic sheet becomes wet and the chaffing on an infant is increased due to the wetness and the spaced-apart position of the folded panels.